The IEA said global electric vehicle sales grew by more than 50 percent from 2016 to 2017. The nearly 580,000 electric vehicles sold in China made up almost half of global sales last year, with the U.S. in second place at about 280,000 electric cars sold in 2017. That’s up from the 160,000 sold in the U.S. in 2016.

Kara Kockelman, a transportation engineering professor at the University of Texas, said those numbers are impressive. But she noted that further growth could be stunted by laws, such as one in Texas, that ban electric car makers like Tesla from selling directly to customers.

“That’s why you don’t see many [electric vehicles] in many showrooms in many places, especially around Texas,” Kockelman said. “So we have to wait a year or more, and do extra legwork to try to get access to these vehicles, and that’s a real hurdle.”

A bigger hurdle, Kockelman said, is the fact that it’s still just much faster to fill up a car with gas than it is to charge an electric car, and Americans don’t like to wait. The IEA report noted that in 2017, only about a quarter of the 430,000 publicly available car chargers worldwide were “fast chargers.”

The report pointed to other challenges as well, like growing demand for lithium and cobalt, key ingredients for electric car batteries that the report described as currently “scarce.”

Still, the report said the industry’s growth has been helped by dropping costs for batteries and improved battery performance, alongside tighter fuel-economy standards and other government policies around the world that push the market toward more environmentally-friendly cars.

The IEA expects those policies to drive electric car sales to 125 million by 2030, though the report said that number could grow to as high as 220 million with more ambitious climate-related policies.